Heretofore, rheostats for use in studio mixers have had a casing in which a pair of resistance base plates each having a resistance layer is disposed in an opposed and parallel relation. A slider support is disposed between the base plates, and the opposite surfaces of the support are provided with sliders which come into resilient contact with the respective base plates. Thus, the resistance value of the rheostat is varied by sliding the slider support.
In the aforementioned rheostat, the sliders which come into resilient contact with the respective base plates have been required to contact the resistance layer portions at areas providing the same resistance value. Accordingly, it is customary to adjust the positions of the sliders to eliminate any interlocking error. However, this adjusting operation is difficult to perform.